1. Field of the Invention
The present invention relates generally to a method of separating Cesium-131 (Cs-131) from Barium (Ba). Uses of the Cs-131 purified by the method include cancer research and treatment, such as for use in brachytherapy implant seeds independent of method of fabrication.
2. Description of the Related Art
Radiation therapy (radiotherapy) refers to the treatment of diseases, including primarily the treatment of tumors such as cancer, with radiation. Radiotherapy is used to destroy malignant or unwanted tissue without causing excessive damage to the nearby healthy tissues.
Ionizing radiation can be used to selectively destroy cancerous cells contained within healthy tissue. Malignant cells are normally more sensitive to radiation than healthy cells. Therefore, by applying radiation of the correct amount over the ideal time period, it is possible to destroy all of the undesired cancer cells while saving or minimizing damage to the healthy tissue. For many decades, localized cancer has often been cured by the application of a carefully determined quantity of ionizing radiation during an appropriate period of time. Various methods have been developed for irradiating cancerous tissue while minimizing damage to the nearby healthy tissue. Such methods include the use of high-energy radiation beams from linear accelerators and other devices designed for use in external beam radiotherapy.
Another method of radiotherapy includes brachytherapy. Here, radioactive substances in the form of seeds, needles, wires or catheters are implanted permanently or temporarily directed into/near the cancerous tumor. Historically, radioactive materials used have included radon, radium and iridium-192. More recently, the radioactive isotopes cesium-131(Cs-131), iodine (I-125), and palladium (Pd-103) have been used. Examples are described in U.S. Pat. Nos. 3,351,049; 4,323,055; and 4,784,116.
During the last 30 years, numerous articles have been published on the use of I-125 and Pd-103 in treating slow growth prostate cancer. Despite the demonstrated success in certain regards of I-125 and Pd-103, there are certain disadvantages and limitations in their use. While the total dose can be controlled by the quantity and spacing of the seeds, the dose rate is set by the half-life of the radioisotope (60 days for I-125 and 17 days for Pd-103). For use in faster growing tumors, the radiation should be delivered to the cancerous cells at a faster, more uniform rate, while simultaneously preserving all of the advantages of using a soft x-ray emitting radioisotope. Such cancers are those found in the brain, lung, pancreas, prostate and other tissues.
Cesium-131 is a radionuclide product that is ideally suited for use in brachytherapy (cancer treatment using interstitial implants, i.e., “radioactive seeds”). The short half-life of Cs-131 makes the seeds effective against faster growing tumors such as those found in the brain, lung, and other sites (e.g., for prostate cancer).
Cesium-131 is produced by radioactive decay from neutron irradiated naturally occurring Ba-130 (natural Ba comprises about 0.1% Ba-130) or from enriched barium containing additional Ba-130, which captures a neutron, becoming Ba-131. Ba-131 then decays with an 11.5-day half-life to cesium-131, which subsequently decays with a 9.7-day half-life to stable xenon-130. A representation of the in-growth of Ba-131 during 7-days in a typical reactor followed by decay after leaving the reactor is shown in FIG. 1. The buildup of Cs-131 with the decay of Ba-131 is also shown. To separate the Cs-131, the barium target is “milked” multiple times over selected intervals such as 7 to 14 days, as Ba-131 decays to Cs-131, as depicted in FIG. 2. With each “milking”, the Curies of Cs-131 and gram ratio of Cs to Ba decreases (less Cs-131) until it is not economically of value to continue to “milk the cow” (as shown after ˜40 days). The barium “target” can then be returned to the reactor for further irradiation (if sufficient Ba-130 is present) or discarded.
In order to be useful, the Cs-131 must be exceptionally pure, free from other metal (e.g., natural barium, calcium, iron, Ba-130, etc.) and radioactive ions including Ba-131. A typical radionuclide purity acceptance criterion for Cs-131 is >99.9% Cs-131 and <0.01% Ba-131.
The objective in producing highly purified Cs-131 from irradiated barium is to completely separate less than 7×10−7 grams (0.7 μg) of Cs from each gram (1,000,000 μg) of barium “target”. A typical target size may range from 30 to >600 grams of Ba(II), (natural Ba comprises about 0.1% Ba-130). Because Cs-131 is formed in the BaCO3 crystal structure during decay of Ba-131, it is assumed that the Ba “target” must first be dissolved to release the very soluble Cs(I) ion.
Due to the need for highly purified Cs-131 and the deficiencies in the current approaches in the art, there is a need for improved methods.